The formation of hydrated lime (Ca(OH)2) is effected by mixing quicklime (CaO) with water, and is an exothermic reaction difficult to control.
Hydrated lime that is used in removal systems to remove sulfur dioxide from gaseous streams are usually required to have a low free moisture content (<2.0%) and BET specific surface areas of about 16-18 m2/g or more, as well as pore volumes in the range of about 0.65-0.80 cm3/g. It has been difficult, previously, to slake lime using conventional slakers to provide consistent results in slaked lime formation that had consistent high specific surface areas and pore volumes.
Some conventional systems for slaking lime to form hydrated lime (FIG. 2) have provided a closed horizontally disposed chamber using one or more Archimedes screw devices (1,2) to move the quicklime and water through the vessel while mixing the same, as schematically illustrated, while other conventional systems (FIG. 3) used spaced shafts with outwardly extending paddles attached thereto, which would mix and move the quicklime and water mixture from an inlet to an outlet of a closed vessel. Such conventional systems, however, have been found to not produce a product with sufficiently consistent properties such as specific surface areas and pore volume from one batch to another.
The need exists for an apparatus and method that will provide a consistent hydrated lime that has a specified specific high surface area and a high pore volume, which product would be useful in removing sulfur dioxide from gases, such as those gases produced in fossil fuel burning power plant systems.